Time-varying association between body mass index and all-cause mortality in patients with hypertension.

BACKGROUND: Relationship between BMI and all-cause mortality in patients with hypertension remains controversial. This study aimed to evaluate the time-varying association between BMI in patients with hypertension and all-cause mortality. METHODS: This population-based cohort study included 212,394 Chinese adults with hypertension from 2007 to 2015 and was followed up until death, loss-to-follow-up, or December 31, 2018. According to the World Health Organization criteria for Asians, BMI was categorized into five groups: underweight (BMI < 18.5 kg/m2), normal weight (18.5-22.9 kg/m2), overweight (23-24.9 kg/m2), class I obesity (25-29.9 kg/m2) and class II obesity (BMI ≥ 30 kg/m2). Cox model was used to estimate the time-varying association of BMI on the risk of mortality by including the interaction term between BMI and time using restricted cubic spline. RESULTS: Compared with normal weight, underweight and class II obesity were associated with higher mortality (Hazard ratio [HRs] at 1 and 10 years of follow-up: 1.51 [95% CI: 1.39-1.65], and 1.27 (1.15-1.41) for underweight, respectively; 1.08 (0.96-1.21), and 1.16 (1.03-1.30) for class II obesity, respectively). However, overweight and class I obesity were associated with lower mortality, although the protective effects gradually attenuated over time (HRs at 1 and 10 years of follow-up: 0.85 (0.81-0.90), and 0.96 (0.91-1.02) for overweight, respectively; 0.80 (0.76-0.84), and 1.04 (0.99-1.10) for class I obesity, respectively). CONCLUSIONS: We found increased mortality among hypertensive patients with underweight and class II obesity while decreased mortality with overweight and class I obesity was observed during the first 5 years of follow-up. Management efforts for hypertension may target controlling body weight in a reasonable range for patients, and probably more attention should be given to underweight patients.